The National Fraud Intelligence Bureau, part of City of London Police, says people are getting calls promising high returns on pension cash if they invest in a space.

The salesmen also often claim they will buy back the spot if the investor no longer needs it. But, in fact, there’s no guarantee of this.

Instead savers risk being lumbered with a strip of concrete in return for their nest egg.

The scam is the latest in a string of dubious investments offered by rogue firms who talk savers into handing over cash they have withdrawn under new pension freedoms.

Because these firms are not regulated by the Financial Conduct Authority, savers risk losing every penny if they fail.

Tom McPhail, head of retirement policy at investment firm Hargreaves Lansdown, says: ‘The lure of large sums of newly accessible pension money is attracting unscrupulous fraudsters out to make a quick buck at someone else’s expense.

‘Investors should never trust cold callers and should only deal with regulated businesses.’